Hoisting ropes for elevators are used to provide the necessary lifting forces and traction forces for moving the elevator car. Hoisting ropes are typically formed from steel wire strands woven together to form the rope. Such hoisting ropes have proven to be very durable and dependable. A drawback to the use of steel wire ropes is their weight. As the rise of the elevator increases, the portion of the load resulting from the mass of the rope increases. This produces a limitation on the rise of the elevator and the required output of the lifting equipment.
Lightweight, non-metallic materials have been suggested to replace the steel wire ropes. High strength, polyaramid materials, such as KEVLAR, are being investigated for use in elevator applications. These ropes would be formed from polyaramid fibers woven to form strands, which are then woven together to form the rope. An outer jacket may then be used to protect the woven fibers from damage and wear, and to provide the necessary traction to move the elevator car.
An area of concern is how to inspect such synthetic ropes to determine if the rope should be discarded and replaced with a new rope. The current inspection methods for steel wire rope includes visually inspecting the rope to determine the number of broken steel wires in a given length of steel rope. If a predetermined maximum number of broken wires is detected, the steel rope is discarded. This method is not applicable to synthetic fiber ropes having an outer jacket.
One previously known method is to place an electrically conductive member within the rope. The status of the conductive member may be tested by applying an electrical current to the member. If damage occurs to an extent great enough to break the conductive member, the electrical circuit is broken. There are several drawbacks to this method. First, there is no assurance that the loss of electrical continuity is the result of damage to the rope. Second, there is no qualitative information to indicate if the rope is degrading during use. The first indication is provided by the broken conductive member.
The above art notwithstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop methods and apparatus to monitor hoisting ropes.